(a) Field of the Invention
The present invention relates to a dry type objective and, more particularly, to a microscope objective with a large numerical aperture and high magnification.
(b) Description of the Prior Art
For a dry type of objective with magnification about 100.times., the larger the numerical aperture (NA) is, the more desirable. Many of this kind of microscope objectives have NA about 0.9. If possible, it is desirable to make NA as large as 0.95. However, when NA is made larger than 0.9, it is difficult to correct aberrations, especially, longitudinal chromatic aberration. This is because the curve of chromatic aberration of spherical aberration becomes very large.
This kind of known microscope objective is disclosed, for example, in Japanese published unexamined patent application No. 75614/81. In case of said objective, however, curvature of field is not corrected satisfactorily and favourable image cannot be obtained up to the marginal portion of the field. Moreover, NA of said objective is 0.9 and this does not fulfill one of objects of the present invention (to make NA larger than 0.9).